Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers
Authors: Mark Loeb, Dominik Mertz, Zain Chagla, John Conly
Journal: Annals of Internal Medicine (2023)

LettersJuly 2023Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care WorkersFREEMark Loeb, MD, Dominik Mertz, MD, Zain Chagla, MD, John Conly, MDMark Loeb, MDDepartment of Pathology and Molecular Medicine and Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, CanadSearch for more papers by this author, Dominik Mertz, MDDepartment of Medicine, McMaster University and Hamilton Health Sciences, Hamilton, Ontario, CanadaSearch for more papers by this author, Zain Chagla, MDDepartment of Medicine, McMaster University, and St. Joseph's Healthcare, Hamilton, Ontario, CanadaSearch for more papers by this author, John Conly, MDDepartment of Medicine, University of Calgary and Alberta Health Services, Calgary, Alberta, CanadaSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/L23-0077 SectionsAboutVisual AbstractPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail IN RESPONSE: Our randomized trial has been described as the best evidence to date comparing medical masks with N95 respirators (1). Several comments have raised concerns, which we address here.One concern raised by Dr. Brosseau and Dr. Hedges and colleagues is a lack of equipoise. The fact that policies about the use of medical masks versus N95 respirators for routine care of patients with COVID-19 varied between jurisdictions is indisputable evidence of equipoise. The trial was conducted only at health care facilities in jurisdictions where wearing medical masks was the policy for routine care of patients with COVID-19. Our study underwent independent peer review by the Canadian Institutes of Health Research; 10 ethics review boards; and the Tri-Council Federal Office Panel, the organization that creates framework and guidance for the ethical conduct of research in Canada. No concerns were noted.A general comment was that complex interventions do not need to be subject to randomized trials as noted by Dr. Greenhalgh and associates and that one could rather rely on mechanistic or laboratory studies, limited observational studies, and a flawed systematic review (2). Observational and mechanistic data can have significant unrecognized biases and real-world implementation issues that can be overcome only by randomization, where the principles of evidence-based medicine prevail in shaping appropriate interventions. There is a legacy of interventions relying on mechanistic data that were reversed on the basis of well-done randomized controlled trials (3).Although Drs. Fisman and Macintyre raised concerns that participants did not adhere to universal masking, we have more than 7500 reports where participants attested to always using the medical mask or N95 respirator they were allocated to over their entire shift. Drs. Fisman and Macintyre also questioned recruitment outside of Canada. The expanded recruitment efforts were justified because we could no longer enroll participants in Canada because of vaccine rollout. The suggestion that we should have stopped the study and conducted an unplanned subgroup analysis does not make sense (4). We increased the sample size to increase the power of the trial and account for participants who could not complete the 10 weeks of follow-up because of mRNA vaccination.Drs. Fisman and Macintyre have also conducted a post hoc power calculation to suggest that our study was underpowered. Power is a pretrial concept; once the trial is completed, the focus should be on the CIs (5). We acknowledged in the article that the noninferiority margin was wide. However, the absolute risk difference was 1.19% (95% CI, –2.5% to 4.9%), values that should be reassuring to physicians and other health care workers. The findings indicate that medical masks may offer noninferior protection to N95 respirators within the types of settings observed in the trial (1).Dr. Delaine is correct to say that medical masks were noninferior to N95 respirators. However, this is not because “their trial did not show superiority” of N95 respirators; it is because the greatest possible difference in effectiveness when comparing medical masks with N95 respirators that is compatible with the data (as determined by the upper limit of the 95% CI) fell within the noninferiority margin. Noninferiority trials test whether an intervention is “not inferior” or “not unacceptably worse” than the intervention used as the control (6). In contrast, equivalence trials are designed to show that 2 interventions do not differ in either direction by more than a specified amount.This study is the only completed randomized controlled trial of surgical masks versus N95 respirators in the setting of COVID-19, an achievement that should be commended in a time of research instability. Some of the less scientifically based comments may discourage future high-quality research during public health emergencies.References1. Chou R. Comparative effectiveness of mask type in preventing SARS-CoV-2 in health care workers: uncertainty persists. Ann Intern Med. 2022;175:1763-1764. [PMID: 36442057] doi:10.7326/M22-3219 LinkGoogle Scholar2. Collins AP, Service BC, Gupta S, et al. N95 respirator and surgical mask effectiveness against respiratory viral illnesses in the healthcare setting: a systematic review and meta-analysis. J Am Coll Emerg Physicians Open. 2021;2:e12582. [PMID: 34746923] doi:10.1002/emp2.12582 CrossrefMedlineGoogle Scholar3. Prasad V, Gall V, Cifu A. The frequency of medical reversal [Letter]. Arch Intern Med. 2011;171:1675-6. [PMID: 21747003] doi:10.1001/archinternmed.2011.295 CrossrefMedlineGoogle Scholar4. Bassler D, Montori VM, Briel M, et al. Early stopping of randomized clinical trials for overt efficacy is problematic. J Clin Epidemiol. 2008;61:241-6. [PMID: 18226746] doi:10.1016/j.jclinepi.2007.07.016 CrossrefMedlineGoogle Scholar5. Goodman SN, Berlin JA. The use of predicted confidence intervals when planning experiments and the misuse of power when interpreting results. Ann Intern Med. 1994;121:200-6. [PMID: 8017747] LinkGoogle Scholar6. Schumi J, Wittes JT. Through the looking glass: understanding non-inferiority. Trials. 2011;12:106. [PMID: 21539749] doi:10.1186/1745-6215-12-106 CrossrefMedlineGoogle Scholar Comments0 CommentsSign In to Submit A Comment Author, Article, and Disclosure InformationAuthors: Mark Loeb, MD; Dominik Mertz, MD; Zain Chagla, MD; John Conly, MDAffiliations: Department of Pathology and Molecular Medicine and Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, CanadDepartment of Medicine, McMaster University and Hamilton Health Sciences, Hamilton, Ontario, CanadaDepartment of Medicine, McMaster University, and St. Joseph's Healthcare, Hamilton, Ontario, CanadaDepartment of Medicine, University of Calgary and Alberta Health Services, Calgary, Alberta, CanadaDisclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M22-1966. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetailsSee AlsoMedical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Mark Loeb , Amy Bartholomew , Madiha Hashmi , Wadea Tarhuni , Mohamed Hassany , Ilan Youngster , Ranjani Somayaji , Oscar Larios , Joseph Kim , Bayan Missaghi , Joseph V. Vayalumkal , Dominik Mertz , Zain Chagla , Maureen Cividino , Karim Ali , Sarah Mansour , Lana A. Castellucci , Charles Frenette , Leighanne Parkes , Mark Downing , Matthew Muller , Verne Glavin , Jennifer Newton , Ravi Hookoom , Jerome A. Leis , James Kinross , Stephanie Smith , Sayem Borhan , Pardeep Singh , Eleanor Pullenayegum , and John Conly Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Christine Laine , Christina C. Wee , Stephanie Chang , Deborah Cotton , Vineet Chopra , Sankey V. Williams , Yu-Xiao Yang , Eliseo Guallar , Eric A. Ross Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Jim Delaine Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Kevin Hedges , Marianne Levitsky , Genevieve Marchand , Lidia Morawska , Luc Bhérer , Marie-Claude Letellier Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Trisha Greenhalgh , Danielle J. Cane , Matthew Oliver Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers David N. Fisman , Raina Macintyre Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers Lisa M. Brosseau Metrics July 2023Volume 176, Issue 7KeywordsCOVID-19Health care providersInfectious diseasesPreventive medicine ePublished: 18 July 2023 Issue Published: July 2023 Copyright & PermissionsCopyright © 2023 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...